Brevetoxin-3 (PbTx-3) and its derivatives modulate single tetrodotoxin-sensitive sodium channels in rat sensory neurons.
Brevetoxin-3 (PbTx-3), produced by marine dinoflagellates (Ptychodiscus brevis), is a lipophilic 11-ring polyether molecule that binds with high affinity to site 5 of the voltage-sensitive sodium (Na+) channel. The effects of PbTx-3 and its derivatives were studied in cell-attached membrane patches on neurons dissociated from neonatal rat nodose ganglia by the patch-clamp technique. PbTx-3 (30-500 nM) produced a shift in activation to more negative membrane potentials whereby single-channel activity was observed under steady-state conditions (maintained depolarization at -50 mV). The unitary current-voltage relationship is linear, which exhibits a reversal potential of approximately +60 mV. Two unitary current amplitudes could be observed in the presence of PbTx-3, with slope conductances of 10.7 pS and 21.2 pS. PbTx-3 inhibits the inactivation of Na+ channels and prolongs the mean open time of these channels. Unitary Na+ currents could be blocked by 1 microM tetrodotoxin (TTX) added to the pipette solution, which indicates that the single-channel currents are caused by the opening of TTX-sensitive Na+ channels. The PbTx-3 molecule is proposed to have multiple active centers (A-ring lactone, C-42 of R side chain) interacting with the Na+ channel binding site. Modification of the molecular structure of PbTx-3 at these centers produced derivatives (PbTx-6, 2,3,41,43-tetrahydro-PbTx-3, 2,3,27,28,41, 43-hexahydro-PbTx-3 and 2,3-dihydro-PbTx-3 A-ring diol), which were less potent than PbTx-3 in producing similar effects on Na+ channel kinetics. PbTx-3 and its derivatives may provide insight into the mechanics of voltage-sensitive Na+ channel gating.
Jeglitsch
G
G
Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Miami, Florida, USA.
Rein
K
K
Baden
D G
DG
Adams
D J
DJ
D000818:Animals; D000831:Animals, Newborn; D004141:Dinoflagellida; D015640:Ion Channel Gating / Q000187:drug effects*; D008387:Marine Toxins / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009466:Neuromuscular Blocking Agents / Q000494:pharmacology; D009620:Nodose Ganglion; D035964:Oxocins; D018408:Patch-Clamp Techniques; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects*; D013329:Structure-Activity Relationship; D000095702:Polyether Toxins
D008387:Marine Toxins; D009466:Neuromuscular Blocking Agents; D035964:Oxocins; D015222:Sodium Channels; C041017:brevetoxin T17; D000095702:Polyether Toxins